Spinal fixation system

ABSTRACT

A spinal fixation system includes a rod, an anchor, and a clamp assembly. The anchor is adapted to engage a bone. The clamp assembly secures the anchor to the rod. The clamp assembly includes a first portion with first and second flanges for receiving the anchor. A compressible ball is carried by the second portion of the clamp assembly. The ball has a through hole receiving the rod. The through hole is defined by a generally cylindrical inner surface having at least one relieved channel. The first and second flanges include first and second opposing surfaces, respectively. The first and second opposing surfaces are normally angled relative to one another. A nut which threadably engages an upper shaft of the fastener is tightened to draw together the first and second flanges to a position in which they are generally parallel to one another. At least a portion of the through hole tapers from one of the first and second ends towards a center of the ball.

FIELD OF THE INVENTION

[0001] The present invention relates generally to the field of spinalfixation devices. More specifically, the present invention is directedto a clamp assembly of a spinal fixation system that couples a rod and abone anchor.

BACKGROUND OF THE INVENTION

[0002] The spinal column is a highly complex structure which houses andprotects critical elements of the nervous system. In spite of thesecomplexities, the spinal column is a highly flexible structure, capableof a high degree of curvature and twist through a wide range motion.Genetic or developmental irregularities, trauma, chronic stress, tumors,and disease, however, can result in spinal pathologies which eitherlimit this range of motion, or threaten the critical elements of thenervous system housed within the spinal column.

[0003] A variety of systems has been disclosed in the art which achieveimmobilization of portions of the spinal column by implanting artificialassemblies in or on the spinal column. These assemblies may be generallyclassified as anterior, posterior or lateral implants. Posteriorimplants are attached to the back of the spinal column generally bycoupling to the pedicles with screws, or through hooks that attach underthe lamina. In either case, the implants generally include elongatesupport rod elements which are coupled to the screws or hooks toimmobilize two or more sequential vertebrae, for example to hold themstable so that adjacent bones may be fused with bone graft.

[0004] During implantation of a spinal fixation system of the typehaving an elongated support rod and anchors, it is important to provideadjustability between the support rod and the anchors. Adjustabilityfacilitates ideal placement of the bone anchors relative to the spine.Preferably, the adjustability between the support rod and the anchorsallows the supports rods to translate relative to the anchors and alsoallows for pivotal movement of the anchors relative to the support rod.The spinal system must also be able to arrest relative movement betweenthe support rod and the anchors after implantation so that the spinalsegments are post-operatively immobilized.

[0005] While known spinal fixation systems have proven to be useful forvarious applications, they are all associated with drawbacks. In thisregard, the fixation screws or hooks of most known systems are difficultor impossible to adequately tighten to arrest relative movement betweenthe anchors and support rod after implantation. Overcoming thislimitation typically involves a complex clamping arrangement or anarrangement that requires undue tightening. Use of known systems areoften a tedious process, which is inconsistent in result and addsunwanted time to a procedure.

[0006] Accordingly, it remains a need in the art to provide an improvedspinal system clamping mechanism for coupling a rod and a bone anchorthat overcomes the above discussed and other drawbacks of the prior art.

SUMMARY OF THE INVENTION

[0007] According to one aspect, the present invention relates to asystem for spinal fixation which includes an improved clamp assembly forsecuring an anchor to a rod.

[0008] It is an object of the present invention to provide a clampassembly for a spinal fixation system that selectively permits relativetranslation and rotation between an anchor and a rod.

[0009] It is another object of the present invention to provide alocking ball design for a spinal fixation clamp assembly that allows formore uniform collapse and thereby increases locking strength independentof the position of the ball.

[0010] It is another object of the present invention to provide a ballof a spinal clamp assembly that does not impinge on a contoured rod.

[0011] In one form, the present invention provides a spinal fixationsystem including a rod, an anchor, and a clamp assembly. The anchor isadapted to engage a bone. The clamp assembly secures the anchor to therod. The clamp assembly includes a first portion for receiving theanchor. A compressible ball is carried by the second portion of theclamp assembly. The ball has a through hole receiving the rod. Thethrough hole is defined by a generally cylindrical inner surface havingat least one relieved channel.

[0012] In another form, the present invention provides a clamp assemblyfor securing a bone anchor to a generally cylindrical rod. The clampassembly includes first and second spaced apart flanges for receiving aportion of a bone anchor. The first and second flanges include first andsecond opposing surfaces, respectively. The first and second opposingsurfaces are normally angled relative to one another. A nut whichthreadably engages an upper shaft of the fastener is tightened to drawtogether the first and second flanges to a position in which they aregenerally parallel to one another.

[0013] In another form, the present invention provides a compressibleball for receiving a generally cylindrical rod of a spinal system. Thecompressible ball cooperates with a clamp body to form a ball and socketjoint. The compressible ball includes a through hole for receiving therod. The through hole extends along an axis and has a first end and asecond end. At least a portion of the through hole tapers from one ofthe first and second ends towards a center of the ball. Preferably, bothends of the through hole taper and a center portion of the through holehas a constant diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a perspective view of a spinal fixation systemconstructed in accordance with the teachings of a preferred embodimentof the present invention, the spinal fixation system shown arranged inan exemplary construct and operatively attached to a human spinalcolumn.

[0015]FIG. 2 is a perspective view of one of the spinal anchors and anassociated clamp assembly of FIG. 1 removed from the construct of FIG. 1for purposes of illustration.

[0016]FIG. 3 is a partially exploded side view of a portion of theconstruct of FIG. 1.

[0017]FIG. 4 is a perspective view of the clamp assembly of FIG. 2.

[0018]FIG. 5A is a side view of the clamp assembly of FIG. 4 shown withthe first and second flanges normally spaced apart.

[0019]FIG. 5B is a view similar to FIG. 5A illustrating the first andsecond flanges drawn together.

[0020]FIG. 6 is a cross-sectional view taken along the line 6-6 of FIG.5A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021] The following description of the preferred embodiments of thepresent invention is merely exemplary in nature and is in no wayintended to limit the subject invention or its application or uses.

[0022] With general reference to the drawings, a spinal fixation systemconstructed in accordance with the teachings of the preferred embodimentof the present invention is illustrated and generally identified atreference character 10. As shown in the environmental view of FIG. 1,components of the system 10 have been arranged in an exemplary constructfor attachment to a portion of a spinal column 12 of a human patient.The components of the system 10 of the present invention used in theconstruct of FIG. 10 generally include a linkage in the form of agenerally cylindrical support rod 14, a plurality of spinal anchors 16for engaging the spinal column 12, and a plurality of clamp assemblies18 securing the spinal anchors 16 to the cylindrical rod 14.

[0023] The spinal anchors are illustrated throughout the drawings asbone screws 16. Alternatively, it will be understood by those skilled inthe art that other types of anchors known in the art may be employed fordirectly engaging the spine. For example, the anchors may alternativelybe hooks that attach under the lamina of the spine.

[0024] With particular reference to FIGS. 2 and 3, one of the spinalanchors 16 and an associated one of the clamp assemblies 18 areillustrated in further detail. The spinal anchor 16 includes an upperthreaded shaft portion 20 and a lower threaded shaft portion 22. Theupper threaded shaft portion 20 threadably engages a nut 24 when thespinal anchor 16 is secured to a linkage or rod 14 in a manner discussedbelow. The rod is preferably a generally cylindrical rod 14.

[0025] The clamp assemblies 18 each adjustably interconnect one of thespinal anchors 16 that engage the spinal column 12 with the rod 14. Inthe exemplary construct of FIG. 1, the system 10 of the presentinvention is illustrated to include three clamp assemblies 18A, 18B,18C. A first of the clamp assemblies 18A is shown in further detail inFIGS. 2-6 and is illustrated to generally include a body 26 having afirst portion 28 for engaging the rod 14 and a second portion 30 forengaging the spinal anchor 16. The body 26 of the clamp assembly 18A isshown to generally have a C-shape with an intermediate portion or armthat defines an opening 32 for receiving the rod 14. In the embodimentillustrated, the opening 32 is partially spherical and is adapted toadjustably receive a compressible locking member or ball 34.

[0026] The compressible locking ball 34 is shown particularly in FIGS.5A and 5B and the cross-sectional views of FIG. 6. As shown, the lockingball 34 is generally spherical in shape and includes an aperture orthrough hole 36 which passes therethrough for receiving the rod 14. Aswill become more apparent below, the clamp body 26 and the ball 34cooperate to form a ball and socket joint that allows pivotal movementof the rod 14 relative to the anchor 16. This pivotal movement is aboutan imaginary center of the ball 34. The locking ball 34 is normallypermitted to universally move within the opening 32. A slit 38 isprovided in the locking ball 34 to facilitate compression of the balland resulting clamping on the rod 14.

[0027] The through hole 36 is defined by a generally cylindrical innersurface. The generally cylindrical inner surface preferably includes atleast one relieved channel 50. In the embodiment illustrated, thecylindrical inner surface is shown to include five relieved channels 50.The particular number of relieved channels 50 will be understood to be amatter of design choice and may vary from that shown in the drawings.The relieved channels 50 allow for a more uniform collapse of thelocking ball 34. In this manner, the locking strength of the clampassembly 18 is increased independent of the position of the ball 34within the partially spherical opening defined by the clamp 34.

[0028] As perhaps most particularly shown in the cross-section view ofFIG. 6, at least a portion of the through hole 36 tapers from a firstend 52 of the through hole 36 to a second end 54 of the through hole 36toward a center of the locking ball 34. As shown, the through hole 36preferably tapers from the first end 52 towards the center and also fromthe second end 54 towards the center. A center portion 56 of the throughhole 36 has a constant diameter. This configuration of the through hole36 allows the locking ball 34 to be loaded and not impinge on acontoured rod.

[0029] In the embodiment illustrated, the through hole 36 passes throughthe center of the locking ball 34. Alternatively, the through hole 36may be eccentric to the sphere defined by the locking ball 34. Byorienting the through hole 36 eccentric to the sphere, adjustments canbe made by rotating the locking ball 34 within the clamp body 26.

[0030] The clamp body 26 further includes a first or upper flange 40 anda second or lower flange 42. In the embodiment illustrated, the upperand lower flanges 40 and 42 are symmetrical about a plane extendingtherebetween. The upper and lower flanges 40 and 42 are shown to begenerally circular in shape. The intermediate portion or arm of theclamp body 26 that extends between the flanges 40 and 42 is disposedradially relative to the upper and lower flanges 40 and 42. The upperand lower flanges 40 and 42 define distinct but aligning apertures 44and 46 (see FIG. 4), respectively. The apertures 44 and 46 are bothassociated with recesses 48 to receive either a nut 24 or a partiallyspherical shaped portion 60 of the screw 16, respectively. In thismanner, it is impossible to put the clamp assembly 18 on the rod 14upside down.

[0031] As shown particularly in FIG. 5A, the first and second flanges 40and 42 are normally spaced apart by a gap. The first and second flanges40 and 42 includes first and second opposing surfaces 62 and 64,respectively. As shown in FIG. 5A, when the first and second flanges 40and 42 are normally spaced apart, the opposing surfaces 60 and 64 areangled relative to one another.

[0032] Upon tightening of the nut 24, movement of the clamp body 26relative to the rod 14 is arrested. Explaining further, tightening ofthe nut 24 serves to draw the upper and lower flanges 40 and 42 togethercausing the intermediate portion of the clamp body 26 to compresssqueeze the locking ball 34 and correspondingly clamp the rod 14.Relative movement is also arrested between the locking ball 34 and theclamp body 26.

[0033] Importantly, the clamp body 26 is formed to include sufficientspacing between the upper and lower flanges 40 and 42 so that the gap 60is always maintained throughout the range of tightening. In this manner,clamping forces are more efficiently transferred to the locking ball 34.The clamp body 26 is illustrated in a fully clamped condition in FIG.5B. As shown, the opposing surfaces 62 and 64 are oriented generallyparallel to one another.

[0034] With particular reference to FIG. 1, the clamp assemblies 18B and18C will be understood to be identical. The clamp assemblies 18B and 18Cdiffer from the clamp assembly 18A in that the second portion 30 istangentially oriented relative to the first and second flanges 40 and42. In other words, the intermediate portion or arm that connects thefirst and second flanges 40 and 42 is offset to one side from a radialposition. This offset allows the rod 14 to be positioned closer to theanchor 16 and reduces the medial lateral profile of the construct.Otherwise, it will be understood that the clamp assemblies 18A-18C areidentical.

[0035] While the invention has been described in the specification andillustrated in the drawings with reference to preferred embodiments, itwill be understood by those skilled in the art that various changes maybe made and equivalents may be substituted for elements thereof withoutdeparting from the scope of the invention as defined in the claims. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment illustrated by the drawingsand described in the specification as the best mode presentlycontemplated for carrying out this invention, but that the inventionwill include any embodiments falling within the description of theappended claims.

What is claimed is:
 1. A fixation system comprising: a rod; an anchorfor engaging a bone; and a clamp assembly for securing the anchor to therod, the clamp assembly including a first portion receiving the anchor;and a compressible ball carried by a second portion of the clampassembly, the ball having a through hole receiving the rod, the throughhole defined by a generally cylindrical inner surface having at leastone relieved channel.
 2. The spinal fixation system of claim 1, whereinthe through hole of the compressible ball extends along an axis and hasa first end and a second end and wherein at least a portion of thethrough hole tapers from one of the first and second ends toward acenter of the ball.
 3. The spinal fixation system of claim 1, whereinthe through hole tapers from the first end toward the center and fromthe second end toward the center.
 4. The spinal fixation system of claim2, wherein a center portion of the through hole has a constant diameter.5. The spinal fixation system of claim 1, wherein the compressible balland the second portion of the clamp assembly define a ball and socketjoint such that the rod is permitted to pivot relative to the clampassembly about a center of the ball.
 6. The spinal fixation system ofclaim 1, wherein the clamp assembly is operative to selectively arrestrelative movement between the anchor and the rod.
 7. The spinal fixationsystem of claim 1, wherein the generally cylindrical surface includes aplurality of relieved channels.
 8. The spinal fixation system of claim7, wherein the plurality of relieved channels extend generally parallelto an elongated axis of the rod.
 9. A clamp assembly for securing a boneanchor to a generally cylindrical rod, the clamp assembly comprising: afirst portion including first and second normally spaced apart flanges,the first and second normally spaced apart flanges both definingapertures for receiving a portion of the bone anchor; a second portion;and a compressible ball carried by the second portion, the ball having athrough hole for receiving the generally cylindrical rod; wherein thefirst and second flanges includes first and second opposing surfaces,respectively, the first and second opposing surface being normallyangled relative to one another.
 10. The clamp assembly for securing abone anchor to a generally cylindrical rod of claim 9, wherein thethrough hole defined by a generally cylindrical inner surface has atleast one relieved channel.
 11. The clamp assembly for securing a boneanchor to a generally cylindrical rod of claim 9 in combination with thebone anchor, the bone anchor having an upper threaded portion extendablethrough the apertures of the first and second flanges and engaging a nutsuch that tightening of nut draws the first and second flanges towardone another and the second portion compresses the ball.
 12. The clampassembly for securing a bone anchor to a generally cylindrical rod ofclaim 9, wherein the first and second opposing surfaces are generallyparallel to one another when the nut is tightened.
 13. The clampassembly for securing a bone anchor to a generally cylindrical rod ofclaim 12, wherein the second portion circumferentially surrounds theball substantially completely when the first and second flanges aredrawn together.
 14. The clamp assembly for securing a bone anchor to agenerally cylindrical rod of claim 9, wherein the generally cylindricalsurface includes a plurality of relieved channels.
 15. The clampassembly for securing a bone anchor to a generally cylindrical rod ofclaim 14, wherein the plurality of relieved channels extend generallyparallel to an elongated axis of the rod.
 16. The clamp assembly forsecuring a bone anchor to a generally cylindrical rod of claim 9,wherein the compressible ball and the second portion of the clampassembly define a ball and socket joint such that the rod is permittedto pivot relative to the clamp assembly about a center of the ball. 17.A clamp assembly for securing a bone anchor to a generally cylindricalrod, the clamp assembly comprising: a first portion for receiving theanchor; a second portion; and a compressible ball carried by the secondportion, the compressible ball having a through hole for receiving thegenerally cylindrical rod, the through hole extending along an axis andhaving a first end and a second end, at least a portion of the throughhole tapering from one of the first and second ends toward a center ofthe ball.
 18. The clamp assembly for securing a bone anchor to agenerally cylindrical linkage of claim 17, wherein the through holetapers from the first end toward the center and from the second endtoward the center.
 19. The clamp assembly for securing a bone anchor toa generally cylindrical linkage of claim 17, wherein a center portion ofthe through hole has a constant diameter.
 20. The clamp assembly forsecuring a bone anchor to a generally cylindrical linkage of claim 17,wherein the compressible ball and the second portion of the clampassembly define a ball and socket joint such that the rod is permittedto pivot relative to the clamp assembly about a center of the ball.